fix: Add explicit UTF-8 encoding to read_text() calls

[TaeBbong]

Summary

• Path.read_text() without encoding uses the system default (e.g. cp949 on Korean Windows, shift_jis on Japanese Windows), causing UnicodeDecodeError when reading UTF-8 files
• Added encoding="utf-8" to all read_text() calls that were missing it:
  • strix/tools/registry.py — XML schema loading
  • strix/skills/__init__.py — skill markdown loading

Solves #302

Error reproduced

Error loading schema file ...\finish_actions_schema.xml:
'cp949' codec can't decode byte 0xe2 in position 2495: illegal multibyte sequence

Test plan

• Verify Strix launches without encoding errors on non-English Windows (Korean, Japanese, etc.)
• Verify no regression on Linux/macOS where default encoding is already UTF-8

[greptile-apps]

Greptile Overview

Greptile Summary

Fixed encoding issues on non-English Windows systems by adding explicit UTF-8 encoding to Path.read_text() calls.

• Added encoding="utf-8" to strix/tools/registry.py:51 - prevents UnicodeDecodeError when loading XML schema files on systems with non-UTF-8 default encoding (e.g., cp949 on Korean Windows)
• Added encoding="utf-8" to strix/skills/__init__.py:133 - prevents UnicodeDecodeError when loading skill markdown files
• All read_text() calls in the codebase have been updated (verified via codebase search)

The changes are minimal, focused, and directly address the reported error without modifying any logic.

Confidence Score: 5/5

• This PR is safe to merge with no risk
• The changes are minimal and surgical - only adding explicit UTF-8 encoding parameters to two read_text() calls. This is a best practice that fixes real encoding errors on non-English systems while maintaining full backward compatibility on systems where UTF-8 is already the default. No logic changes, no new dependencies, and the fix directly addresses the documented error.
• No files require special attention

Important Files Changed

Filename	Overview
strix/tools/registry.py	Added UTF-8 encoding to XML schema file loading to prevent UnicodeDecodeError on non-English systems
strix/skills/init.py	Added UTF-8 encoding to skill markdown file loading to prevent UnicodeDecodeError on non-English systems